Forming and pressure dies for pipe-bending machines



A.- HELLWIG 2,955,638 FORMING AND PRESSURE DIES FOR PIPE-BENDINGMACHINES Oct. 11, 1960 Filed Feb. 5, 1958 INVENTOR. AueusT HELLWIGUnited States Patent "ice FORMING 'AND PRESSURE DIES FOR PIPE-BENDINGMACHINES August Hellwig, Chicago, 111.; Frank P. Hellwig,

administrator of said August Hellwig, deceased Filed Feb. '5, 1958, Ser.No. 713,330

2 Claims. (Cl. 153-32) This invention relates to improvements inpipe-bending machines. 'More specifically, it relates to improvements inthe forming dies and wiping members or follow bars of such machines.

Existing dies result in two disadvantages. One is the flattening of thebent pipe into elliptical section, a form heretofore referred to asfinal. Another is the indentation of the pipe, in which the outline ofthe forming die is impressed into the pipe, particularly at the startingportion of the bend.

It is an object of this invention to provide improved forming dies andfollow bars, adapted to form bends of true circular section and free ofindentation.

It is another object to provide means whereby the bending force isapplied initially at a pre-determined point with respect to the fulcrumof the bend, and thereafter applied at varying points determinedindependently of the judgement or skill of the operator.

Still another object is to provide dies with novel grooves,

dimensioned in accordance with a newly discovered prin- .ciple hereindescribed.

Other objects and advantages of the invention are explained withreference to the accompanying drawings, of which:

Figure 1 is a fragmentary plan view of a commercial pipe-bendingmachine.

Figure 2 is a plan view on a larger scale, of the improved fonning dieand follow bar, shown in their relative starting positions.

Figure 3 is a sectional view, taken on the line 3-3 of Figure 2.

Figure 4 is a plan view similar to Figure 2, showing the improvedforming die and follow bar after advancing operatively.

Figure 5 is a sectional view, taken on the line 5--5 of Figure 4.

Figure 6 is a diagrammatic view, illustrating the dimensioning of thenovel grooves.

It should be understood at the outset, that the present invention isconcerned solely with the co-operation of the forming dies and followbars, and that other elements are shown and described only 'as they areincidental. With this in mind, Figure 1 illustrates a commercialpipebending machine such as is used to bend thin-wall electricalconduit. It comprises in part, the body 10 of a hydraulic ram, to whichlinks 11 are att-ached'by studs 12. Apin 13 rotatably supports a roller14. Bearing against this roller is a follow bar 20' provided with alongitudinally extending groove 21, dimensioned to accommodate a pipe P.

A plunger 15 is pivotally attached by a pin 16 to a .tached'by a pin 18to the forming-die Patented Oct. 11, 1960 the forming die 30', whichcarries the pipe around with it, and forms a bend nesting in the arcuategroove 31'. This process is well known to those skilled in the art ofbending pipe.

Existing forming dies and mating follow bars are commonly made with acombined depth of grooves which measures less than'the diameter of thepipe, as indicated at 19. This aggravates the inherent tendency of thepipe to flatten. Also, it was heretofore believed essential to restrictminutely, the portion of the pipe being worked, so that drawingof themetal occurred rather than bending. A characteristic result is theindentation of the pipe, particularly at the starting portion of thebend, in which the outline of the forming die is noticeably impressed inthe pipe.

The co-action of several improvements serves to overcome thesedisadvantages. Looking now at Figures 2 and 3, the improved follow bar20 has a groove 21 bordered by flat portions 22. These serve as rails,on which the die 30 rolls. Starting at the end 23, the rails slope at asmall angle to an intermediate point 24. The groove 21 is deepest at theend 23, and decreases gradually in depth to the point 24. For theremaining length of the follow bar 20, the groove 21 is of uniformdepth.

At the start of a bending operation, the peripheral edges 32 of theforming die bear against the rails 22 near the deeper portion of thegroove .21. The excess depth affords a space as indicated at 25.Obviously there is no force. tending to crush the pipe.

As shown in Fig. 2, the normal 33 passes through the point 26, a fewdegrees from the start of groove 31. The pipe P is shown at a smallangleto the groove 21. This situation occurs when sufiicient force isexerted to flex the pipe longitudinally to its yield point, but withoutcausing permanent bending.

The pipes impingement in groove 31 terminates at point 26. This point isreferred to as the momentary fulcrum, against which the pipe is bent.Further bending results in advancing the terminus of the bend, with acorresponding advance of the momentary fulcrum.

Heretofore, the pipe was closely confined by the combined grooves of theforming and pressure dies, and force was exerted by the pressure die ata point substantially coincident with the momentary fulcrum, withoutfirst flexing a substantial portion of the pipe. The result is more of adrawing of the metal than one of bending.

In the present invention, as shown in Fig. 2, the pipe is fiexed in along curve, extending from the starting end of the pressure die to apoint 28. A normal through this point intersects the opposite side ofthe pipe at 27, and defines an angle of 15 with the normal 33 It isapparent that in this situation bending force is applied at a point 28which is 15 removed from the momentary fulcrum 26. As a result, the pipeis flexed into a long curve, longitudinally equivalent to a 15 are.

As the forming die rolls further along the pressure die, the anglebetween the momentary fulcrum and the point at which force is applied,gradually decreases. When the forming die has rotated 15, it assumes theposition shown in Fig. 4. The normal 55, drawn through the momentaryfulcrum, simultaneously passes through the 'point 28 in the forming die,defining the point at which When the plunger 15 is caused to advance, itrotates bending force is exerted. Thereafter, until the completionof thebend, this relationship remains constant.

'The present invention limits the flexing of the pipe to an initialportion of the bending cycle, during which the flexed portion of thepipe decreases in length until the momentary fulcrum is substantially inline with the point at which force is exerted by the pressure die. Ifthe flexing is permitted to extend throughout the bending cycle, or to aportion substantially exceeding at 15 arc, the resultis a wrinkling ofthe pipe. Limiting the flexing as described is significant, becausewhile some older bending devices are provided with means for adjustingthe initial position of the follow bar with respect to the fulcrum, thepresent invention is the first'to provide for the pre-determined andautomatic variation of this relationship.

As an example, for bending thin-wall conduit of 1%" trade size, theadded depth of the groove at the end 23 is The length of the inclinedportion of the rails, from the end 23 to the point 24 is 3". For pipesof other diameter, material or wall-thickness, the length and rise ofthe inclined portion of the rails 22 may be determined experimentally.

Older forming dies and follow bars were made-with grooves which, besidesbeing less in depth than the diameter of the pipe, were also greater inwidth. This was done to accommodate the pipe after it had been permittedto flatten.

Other dies have been dimensioned to form bends which are permanently andsubstantially flattened in the plane of the bend. While such bends maybe adaptable to particular applications, they do not conform to the trueroundness which has been the long-sought object of most pipe-bendinginventions.

It is well known that a pipe or tube may easily be compressed orflattened. Beyond this bare fact, no data has ever been compiled of theextent to which various sizes of pipes may be laterally compressedwithout permanent distortion. Neither has lateral compressibility beenpreviously recognized as the determining factor in dimensioning thegrooves of forming dies to an optimum value.

I have discovered that there is, for every right section of pipe, alateral elastic limit which bears a direct relationship to the bendingof the pipe, and to the correct dimensioning of the grooves in theforming dies. Moreover, I have discovered a simple method fordetermining this lateral elastic limit.

If a short piece of pipe is clamped between the jaws of a machinistsvise, it may be measured while being subjected to increasingly greatercompression. It is a simple matter to determine in this manner, theultimate compression from which the pipe still resumes its full diameterupon release. Both the minor and major axis are recorded at the ultimatecompression.

The minor axis determines the correct width of the groove in the formingdie. The major axis determines the correct depth of the combined groovesin the forming die and follow bar. A few thousandths of an inch may beadded to both the width and depth, as a safety factor. Thisdimensioning, as well as a further novelty in the grooves, isillustrated in Figure 6.

The groove 31 is formed with a true semi-circle as the base, withtangent portions T extending therefrom. The diameter of the semi-circleis equal to the minor axis described above. The tangent portions T areso dimensioned that the total depth of the groove 31 is sixtenths of themajor axis. Heretofore it has always been customary to make the groovesin the forming die and follow bar of equal depth. The purpose of theadditional depth of groove in the novel forming die is to insure thatthe pipe is confined laterally before it bottoms in the groove, so thatit cannot flatten when flexed at the beginning of the bending operation.

The groove 21 is formed as the arc of a circle having the same radius asthe groove 31, and having a depth of four-tenths of the major axis. Thisis substantially equal to an arc of 144 degrees.

The combined grooves 21 and 31 encircle the pipe at whatever point thefollow bar 20 bears against the forming die 30. It will be understoodthat the groove 21 is deepened in the inclined portion of the follow baras previously explained.

"Bends formed by the co-operation of the improved forming die and followbar are of true circular section. -If at any portion of a bend,measurements are taken of the diameter in the plane of the bend andlateral thereto, the difference between such measurements will notexceed the accidental variations similarly measured at unbent portionsof the pipe.

The invention has been described with reference to an illustrativepipe-bending machine, and with particular means for varying the positionof the pressure die with respect to the fulcrum ofthe bend. Obviouslythe advantages extend to other pipe-bending machines, and to alternativemeans for varying the relative position of the pressure die.

It is therefor not the intention to limit the invention to theparticular embodiment herein described. Rather, the intention is toinclude all such variations and alternative embodiments and adaptationsas fall Within the spirit of the invention, and of the appended claims.

I claim:

1. A pipe-bending machine comprising, in combination, a pressure diehaving an initial pressure application end, a final pressure end, andsidewalls therebetween defining a groove adapted to partially receive apipe to be bent, said pressure die groove being of true semi-circularconfiguration bordered by flat surface portions adapted to serve asrails running thelength of said groove, a forming diehaving a curvedsurface provided with sidewalls at the periphery thereof defining agroove adapted to cooperate with said pressure die by circumferentiallyenclosing said pipe while said curved surface bears upon the rails ofsaid pressure die, said forming die groove being of true semicircularconfiguration terminating in tangential flats at the inner portions ofthe sidewalls, means pivotally attached to said forming die tangentiallyholding said pipe in the forming die groove, and means for rotating saidforming die whereby said pipe is carried around to form a bend nestingin the curved groove of said forming die, each of said grooves having awidth equal to about the minor compressive axis of said pipe, the depthof said forming die groove plus tangential flats being equal to about0.6 of the major compressive axis of said pipe and the depth of saidpressure die groove being equal to about 0.4 of the major compressiveaxis, said rails sloping at a small angle from said initial pressure endto a point intermediate said initial pressure end and said finalpressure end to provide therebetween a groove of depth slightly greaterthan about 0.4 of the major compressive axis, whereby the initialbending force can be applied to a pipe at a point along its lengthsubstantially removed from the point of first impingement on the formingdie so that a greater portion of the pipe can be worked initially, whilethe point at which the pressure die exerts force is being automaticallyvaried to gradually change the bending force to a drawing force.

2. A pipe-bending machine comprising, in combination, a pressure diehaving an initial pressure application end, a final pressure end, andsidewalls therebetween defining a groove adapted to partially receive apipe to be bent, said pressure die groove being bordered by flat surfaceportions adapted to serve as rails running the length of said groove, aforming die having a curved surface provided with sidewalls at theperiphery thereof defining a groove adapted to cooperate with saidpressure die by circumferentially enclosing said pipe while said curvedsurface bears upon the rails of said pressure die, said forming diegroove terminating in tangential flats at the inner portions of thesidewalls, and means for rotating said forming die whereby said pipe iscarried around to form a bend nesting in the curved groove of saidforming die, each of said grooves having a Width equal to about theminor compressive axis of said pipe, the depth of said forming diegroove plus tangential .flats being equal to about 0.6 ofthe majorcompressive axis of said pipe and the depth of said pressure die groovebeing equal to about 0.4 of the major compressive axis, said railssloping at a small angle from said initial pressure end to a pointintermediate said initial pressure end and said final References Citedin the file of this patent UNITED STATES PATENTS Stephens Nov. 28, 1882Abramson et a] Nov. 21, 1933 FOREIGN PATENTS Canada .u. May 17, 1949Canada Oct. 1, 1957

